Production of high purity crystalline dextrose



Patented Apr. 4, 1939 UNITED STATES- PATENT OFFICE PRODUCTION OF HIGH PURITY CRYSTAL- LINE DEXTROSE No Drawing. Application May 11, 1936, Serial No. 79,177

8 Claims. (Cl. 127-58) This invention relates to the-production of high purity crystalline dextrose, particularly dextrose hydrate, from' starch converted dextrose solutions by methods involving subjecting the mother liquor or first greens from the centrifuging of the massecuite of a first crystallizing operation to a second crystallizing operation in order to obtain a second yield of crystals or second sugar from the original batch of 10 solution; and the object of the invention is to provide a more convenient and economical method than has been available heretofore, for treating the second sugar, which will ordinarily contain a considerable quantity of impurities, for the production therefrom of a crystalline dextrose of 100% purity or a purity closely approximating 100%.

United States patents to W. B. Newkirk, No. 1,471,347, October 23, 1923, and No. 1,521,830,

January 6, 192.5, disclose methods of producing crystalline dextrose, especially the hydrate, according to which mother liquors are crystallized for the purpose of increasing yields. The crystalliaations take place .in crystallizers provided with slow motion agitators and supersaturation is maintained by temperature reduction as crystallization proceeds, These patents contemplate the production of second sugars having purities closely approximating 100%. However, with the improvements in technique it has been found possible, using the patented methods, to obtain larger yields of first sugars with the result that the purity of the second sugars has in practice been considerably reduced. Ordinarily second sugars, according to more recent procedures, will have a purity, or dextrose content, dry substance basis, of about 95%. A higher purity might be obtainedlby excessive washing in the centrifugals but at the unwarranted cost entailed by the excessive loss ofsugar in the wash-water with the disadvantage of erosion of the crystals, impairing the quality of the sugar, due to such excessive washing. It hasconsequently been customary to melt up second sugars and combine the syrup with fresh converted solution going to the first crystallizers. The practice has been to melt the second sugar with water and refine the melt by an adsorption treatment, for example, by filtration through bone black, either before the -melted sugar is mixed with the liquor from the converters, or to combine these liquors and subject the mixture to the refining operations.

The present invention provides an improved, simplified and economical method of treatingrelatively impure second sugars, or other dextrose sugars of like character, so as to give a high purity product, without excessive washing losses and without excessive erosion, the method consisting essentially, in mixing with the second sugar, after it has been centrifuged, a dextrose 5 solution of such character as to wash oi the mother liquor (second greens) from the crystals without dissolving the crystals to any extent so as to give a massecuite of crystals and dextrose ,solution in which the solution will have a purity 0 substantially higher than the purity of the second greens, whereby the sugar in the centrifugal machines may be washed to a high purity with a minimum amount of water, and hence a minimum loss by the dissolving of sugar in the wash 15 water. The mixing is done preferably in an ordinary crystallizer with helicoidal agitator; and preferably the conditions are such that some crystallization of dextrose in solution takes place by deposit on the already formed crystals but 20 without any appreciable induction of new crystals. This crystallization which is brought about by quickly forcing down the temperature of the mass by circulation of cold water through the water jacket of the crystallizer, is intended pri- 25 marily to repair, so to speak, any crystals which may be broken in'the mixing operation.

The solution added to the second sugar must have a gravity such that when it is mixed with the residual second greens adhering to the sugar 30 crystals, the mixture will at least be saturated so that there will be no dissolving of crystalline dextrose. The added solution should have a purity sufiiciently high--the higher the betterso that when the massecuite is again centrifuged 35 the mother liquor, which is a mixture of the added solution and residual second greens, will have a purity sufilciently higher than that of the second greens so that the final produced sugar can be given the desired high purity, say 99.5%-100%, 40 by a, washing operation involving minimum erosion of the crystals and loss of sugar in the wash water.

Preferably the second sugar, after spinning to remove as far as possible the second greens, is 45 not, according to the present invention, washed with fresh water, since the desired high purity cannot be obtainedby mere washing without excessive erosion and sugar losses. However, it might be possible to give the second sugar a brief 50 washing in the centrifugal machine to remove some of the residual greens not removable by mere centrifuging.-

The second sugar,'after the first centrifuging operation will ordinarily contain about solid 55 sugar and 15% hydrol on dry substance basis. The hydrol purity may be about 70%, and the water content of the second sugar from the centrifugals (sugar and second greens) about 13 15%, including water of crystallization the sugar being dextrose monohydrate.

The mixture of second sugar and dextrose solution will ordinarily be run into the crystallizer at a temperature of approximately 100 F. This temperature is reduced to about 78-80 during the mixing and crystallizing operation, which may require from 48 to 60 hours, during which period the temperature of the mass is forced down quite rapidly, in comparison with usual dextrose crystallizing practice, by circulation of 1vivater through the water jacket of the crystalzer.

At the end of this operation the massecuite is drawn off .into centrifugal machines, the mother liquor spun oil? and the sugar washed with fresh water in the usual manner.

The following are specific examples illustrating typical operations:

Example I The second sugar has a purity of 96.1% and a moisture content of 13.2%, including water of crystallization, the percentage of dry substance being therefore 86.8.

The dextrose solution used consists of a first centrifugal wash water, refined by filtration through bone char and concentrated to a density of 33.3 Baum at 100 F. or approximately a dry substance content of 61.0%. The purity is 84.4%.

The solution is mixed with the sugar in proportion of 35% of the dry substance in the solution to 65% dry substance solid sugar.

This will give a fillmass having a dry substance content of 75.6% and a purity of 93.0%. 105,000 pounds of the fillmass is run into the crystallizer at a. temperature of about 100 F. This temperature is reduced in fifty-four hours to 78 F. whereupon the massecuite is discharged to the centrifugal machines. The temperature reduction is effected by practically continuous circulation of cooling water through the jacket of the crystallizer begun a few hours after the crystallizing operation commences.

The sugar after centrifuging and washing with fresh water has a purity of between 99.5% and 100%.

Example II The operating data are the same as in Example I except that a purity converter liquor is mixed with the second sugar, and this, because of its higher purity still further shortens the purging time, and reduces erosion and sugar loss in the wash water.

Obviously the above examples are merely typical and illustrative, and are not to be considered as limitations on the invention. The dry substance content of the fillmass mayvary for example from 74.5% to 77.0%. The purities and moisture contents of the solution will depend,

. naturally, upon the purity and moisture content of the second sugar which may vary to some extent. The proportion of solution to second sugar may for instance vary between 30 and 40 dry substance inthe sugar liquor and 70%-60% dry substance crystalline dextrose. The purity of the second sugars or other sugars suitable for treatment according to this invention will vary ordinarily between 92.5% and 97.5% and their water contents between 13.0% and 15.0%, including water of crystallization. The purities and densities of the dextrose solution used will depend upon the purity and water content of the crystalline dextrose with which it is mixed, and may vary between limits as follows: purity 84.0% to 92.0%; density 31.0 to 34.0 Baum. The ini'tial temperature of the fillmass which will be determined by the temperature to which the added solution is heated may vary from F. to 105 F. The final temperature may vary between 75.0 F. and. 82.0 F., and the crystallizing time between 36 and 96 hours, depending on spinning quality of second sugar (sugar and second greens), and the purity of the solution mixed therewith.

The intention is to cover all modifications within the scope of the appended claims.

I claim: Y

1. Process of treating relatively impure crystalline dextrose containing (after removal of the major portion of the mother liquor of the massecuite) residual mother liquor, for the production of a high purity dextrose which comprises: mixing with the impure crystalline dextrose a dextrose solution having a density sufficiently high to prevent dissolving the solid phase dextrose and a purity substantially in excess of that of the residual mother liquor under conditions such that some crystallization of dextrose in solution takes place by deposit on the already formed crystals; and after the solution is thoroughly commingled with the solid phase dextrose, extracting the solution from the crystalline dextrose.

2. Process of treating relatively impure crystalline dextrose containing (after removal of the major portion of the mother liquor of the massecuite) residual mother liquor, for the pro- "duction of a high purity dextrose which comprises: mixing with the impure crystalline dextrose a dextrose solution having a density sufiiciently high to prevent dissolving the solid phase dextrose and a purity substantially in excess of that of the residual mother liquor; reducing the temperature of the fillmass while the mixing operation proceeds so as to bring about supersaturation of the solution and growth of the crystals in the fillmass; and after the solution is thoroughly commingled with the solid phase dextrose, extracting the solution from the crystalline dextrose.

3. Process of treating relatively impure crystalline dextrose hydrate containing (after removal of the major portion of the mother liquor of the massecuite) residual mother liquor, for the production of a high purity dextrose which comprises: mixing with the impure crystalline dextrose a dextrose solution having a density sufficiently high to prevent dissolving the solid phase dextrose,

' a purity substantially in excess of that of the residual mother liquor, and a temperature such as to give to the mixture a temperature in the neighborhood of 100 F.; reducing the temperature of the fillmass during the mixing operation so as to bring about supersaturation of the solution and growth of the crystals in the fillmass; and then extracting the mother liquor from the crystalline dextrose.

4. Process of treating relatively impure crystalline dextrose hydrate containing (after removal of the major portion of the mother liquor of the massecuite) residual mother liquor, for the production of high purity dextrose which comprises: introducing into a water jacketed crystallizer, having an agitator, at a temperature of approximately 100 F. a mixture of the impure dextrose with a dextrose solution having a density sumciently high to prevent dissolving the solid phase dextrose and a purity substantially in excess of that of the residual mother liquor; agitating the fillmass and reducing the temperature thereof by circulation of cold water through the water jacket of the crystallizer; and extracting the mother the proportion 60-70 dry substance crystalline.

dextrose and -30 dry substance in the solution; supersaturating the fillmass'during the mixing operation tobring about a growth of the crystals in the fillmass without substantial induction of new crystals; and then extracting the mother liquor from the crystalline dextrose.

6. The process of making high purity crystalline dextrose hydrate from a starch converted dextrose solution in which the converted liquor is subjected to successive crystallizing operations which comprises: mixing with the second sugar, containing some second greens, a dextrose solution having a purity between 84% and 92%, a density between 31 and 34 Baum, and a temperature to give the fillmass a temperature of approximately 100 F. in the proportion -70 dry substance crystalline dextrose and 40-30 dry substance in the solution; reducing the temperature of the fillmass during the mixing operation to approximately 78-80 F.; and extracting the mother liquor from the crystalline dextrose.

7. Process of treating crystalline dextrose having a purity between 92.5% and 97.5% to increase the purity of the sugar which comprises: mixing the dextrose'with a dextrose solution having a purity between 84% and 92%, and a density between 31 and 34 Baum in proportion of 60-70 dry substance crystalline dextrose and 40-30 dry substance in the solution; reducing the temperature to bring about growth of the crystals without substantial induction of new crystals; and after the solid phase dextrose and dextrose solution have been thoroughly commingled, extracting mother liquor from the crystalline dextrose.

8. Process of producing high purity crystalline dextrose hydrate from a starch converted dextrose solution by crystallization with temperature reduction and slow motion agitation which comprises: subjecting the converted liquor to a crystallizing operation and centrifuging the massecuite for a yield of first sugar; subjecting the first greens in a refined and concentrated state to a crystallizing operation and centrifuging the massecuite to give a yield of second sugar having a purity of between:92.5% and 97.5% and a water content of between 13% and 15%; mixing with the second sugar a dextrose solution having a purity of between 84% and 92% and a density of between 31 and 34 Baum, in the proportion of 60-70% dry substance crystalline dextrose to 40-30% dry substance in the solution with the solution at a temperature to give the mixture a temperature of approximately F.; reducing the temperature of this fillmass to about 78-80 F. while continuing the mixing operation; and centrifuging the massecuite and washing the sugar with water.

CHARIES J. COPLAND. 

